Generally, microprocessing is performed during a lithography process using a resist composition while semiconductors are manufactured. In the lithography process, a resolution may be improved by reducing the wavelength as shown in Rayleigh Equation in respects to a diffraction limit. Therefore, the wavelength of the light source for lithography process that is used to manufacture semiconductors has been reduced in the order of g-line (wavelength 436 nm), i-line (wavelength 365 nm), KrF-excimer laser (wavelength 248 nm), and ArF-excimer laser (wavelength 193 nm).
In recent years, the integration of integrated circuits has increased, accordingly, the demand for the submicron pattern has also increased. In particular, a photolithography process that uses a KrF-excimer laser or an ArF-excimer laser is noticed because 64-M to 1G DRAMs can be manufactured by using the photolithography process. Meanwhile, color filters are also used with photoresists and require micropatterns. However, a lens of an exposing device using an excimer laser having a short wavelength has a shorter lifespan as compared to a known lens that is used as a light source for exposure. Thus, it is preferable to expose the lens to the excimer laser over a short period of time.
In the related art, a novolac-based resin is the main component of a photoresist composition, which can be used to perform an exposure process by using g-lines (436 nm) and i-lines (365 nm).
According to the Lambert-Beer law, the absorbance is in proportion to a transmission length and a concentration of species absorbing light. Thus, if the concentration of species absorbing light is reduced, the total absorbance is reduced and the transmissivity of the photoresist is increased.
FIG. 1 is a graph illustrating light transmissivity according to a wavelength of a known non-chemically amplified photoresist that contains a novolac-based resin and a photosensitizer. The x-axis denotes the wavelength (unit: nm) and the y-axis denotes light transmissivity (unit: %).
With reference to FIG. 1, light transmissivity is reduced at a short wavelength of 248 nm or less by geometric progression. Since the known non-chemically amplified resist has poor light transmissivity at a short wavelength of 248 nm or less, it is unsuitable for using at a short wavelength of 248 nm or less.
Therefore, in the case of the g-line and i-line photoresists that are used as the known non-chemically amplified resist, it is difficult to form semiconductor micropatterns during KrF (248 nm) semiconductor exposure that is mainly used in the current industrial field because of high absorbance and low sensitivity. Thus, in the current industrial field, the g-line and i-line photoresists are not used for the exposure at a short wavelength of KrF or less.
Accordingly, the demand for a novolac-based resin having high light transmissivity at a short wavelength of 248 nm or less is growing.
Meanwhile, a chemically amplified photoresist containing a photoacid generator is used for the exposure at a short wavelength of KrF or less. The chemically amplified resist contains main components of a PHS polymer and a photoacid generator, and a reaction prohibitor to improve contrast and control solubility. In respects to the development of photoresist material, chemical amplification has been introduced as new concept, in views of chemical mechanism and its use in resists. Chemical amplification means that active species generated by one photon are subjected to chemical chain-reaction to significantly increase the quantum yield. In chemical amplification, the active species that are generated by a single photochemical reaction function as a catalyst to continuously incur chemical reactions such as deprotection and crosslinking. Thus, the total quantum yield of the above-mentioned reactions is significantly increased as compared to the quantum yield when the catalyst is produced at an early stage.
When the chemically amplified resist is used, an acid that is generated by a photoacid generator in a exposed portion is diffused by post exposure bake. In this connection, the solubility of the exposed portion to an alkali developing solution is changed by the reaction using the acid as the catalyst to form positive-type or negative-type patterns. Meanwhile, since the chemically amplified resist contains the acid used as the catalyst, if a substrate has a basic property, tailing occurs at a lower portion of a profile due to deactivation of the acid.
The above-mentioned problems can be avoided by adding a great amount of base-removing substance. However, if a great amount of base-removing substance is used, the sensitivity is reduced. When an excimer laser is used as a light source for exposure, a substrate having low reflectivity is used to significantly improve dimensional uniformity. However, the resist pattern has a tapered profile. Accordingly, the chemically amplified resist is problematic in that its performance and profile depend on the type of substrate.
Among positive type chemically amplified resists, the positive type resist for KrF excimer laser photolithography is made of a poly(hydroxystyrene) resin. Generally, the positive type resist for KrF excimer laser photolithography includes a resin that is protected by a part of phenolic hydroxy groups dissociated by the acid in conjunction with a photoacid generator. In the resolution or sensitivity, the groups which are dissociated by the acid form acetal bonds along with oxygen atoms resulting from the phenolic hydroxy groups. In this connection, a resin that includes tetrahydro-2-pyranyl, tetrahydro-2-furyl, or 1-ethoxy ethyl bonded with oxygen atoms is noticed. However, when the resin is used in metal and implant processes, there is a problem in that a profile is undesirable because the film is thick and the pattern is formed under a special substrate condition.
Generally, an HF etching process is performed during a semiconductor process. However, in the case of the chemically amplified PHS photoresist, the HF etching process cannot be used because of low resistance thereof.